This invention relates generally to coordinating power delivery to critical and non-critical loads of a building or similar structure during main or primary power failure. More particularly, the present invention is directed to a transfer switch that allows circuits of a load center to be connected to an auxiliary power source when primary power fails.
A building, such as a home or other dwelling, will present critical and non-critical loads to the primary power source to the building, which is generally a utility power supply. The critical loads for a home, for instance, may include the HVAC system, sump pump, refrigerators, freezers, dishwasher, washer/dryer, and life-sustaining medical equipment. All other loads of the home will generally be considered non-critical. The non-critical loads are generally connected to non-critical branches that are hardwired to a load center and the critical loads may be connected to critical branches that are hardwired to a separate subpanel; both of which are powered by the primary power source during normal primary power source operation.
To ensure power to the critical loads during primary power source failure, it is known to connect the subpanel and, thus, the critical loads, to an auxiliary power source, such as electrical generator. This connection of the subpanel to the auxiliary power source may be done automatically by an automatic auxiliary power supply system that detects primary power source failure and automatically starts an auxiliary power source, such as an electrical generator, when primary power source failure is detected. The automatic auxiliary power supply system also includes an automatic transfer switch that switches over connection of the subpanel to the auxiliary power source generator. In this regard, the subpanel is connected to the primary power source and the auxiliary power source through a transfer panel that contains the automatic transfer switch. In some installations, the automatic transfer switch and the subpanel are both contained within the transfer panel.
Conventional transfer switches connect only the circuits hardwired to the subpanel to the auxiliary power source. In this regard, during operation of the auxiliary power supply system, it is not possible for an operator, such as a homeowner, to power a non-critical load with the auxiliary power source in the event the homeowner happens to be home when the primary power source fails. For instance, with conventional automatic transfer switches, a homeowner cannot temporarily connect a non-critical load, such as a television or radio, to the auxiliary generator when the primary power source fails.
One proposed automatic transfer switch is disclosed by Hinks, U.S. Pat. No. 6,563,233, which allows an operator to manage, or utilize auxiliary power for energizing a load center circuit through manipulation of a manual feedback breaker and main branch breakers. More particularly, Hinks describes a system whereby a normally closed manual feeder breaker connects the primary power source to the subpanel during normal primary power source operation. When the primary power source fails, the automatic transfer switch activates the auxiliary power source. In order to connect the load center to the auxiliary power source, the operator may manually close a normally open manual feedback breaker, which supplies power to all circuits of the load center. However, in the system described by Hinks it is possible for the normally closed manual feeder breaker and the normally open manual feedback breaker to both be closed at the same time, which can result in the entire load center being automatically connected to the auxiliary power source when the auxiliary power source is subsequently brought online, which not only is in violation of the U.S. National Electrical Code but also likely results in a load that exceeds the capacity of the generator. That is, the system described by Hinks allows those circuits of the load center having closed main branch breakers to be automatically connected to the auxiliary power source when the normally open manual feedback breaker is closed. To avoid circuits of the load center from being connected to the auxiliary power source upon closing of the manual feedback breaker, the operator must individually open each of the conventional main branch breakers for those load center circuits. Additionally, Hinks describes the need for a “second” main breaker to avoid backfeeding of the primary power source when the auxiliary power source is supplying power to the load center.
Therefore, it is desirable to have an automatic transfer switch that is capable of connecting a main or non-critical circuit to an auxiliary power source during primary power failure in a manner that is compliant with the U.S. National Electrical Code. It is also desirable to have a transfer switch that is isolated from the primary power source when a load center circuit is connected to the auxiliary power source so that the transfer switch does not sense auxiliary power as primary power. It would be further desirable to have a transfer switch that does not backfeed the primary power source when a load center circuit is connected to the auxiliary power source.